Ion-Exchange Loading Promoted Stability of Platinum Catalysts Supported on Layered Protonated Titanate-Derived Titania Nanoarrays

Xingxu Lu; Wenxiang Tang; Shoucheng Du; Liaoyong Wen; Junfei Weng; Yong Ding; William S Willis; Steven L Suib; Pu-Xian Gao

doi:10.1021/acsami.9b04378

Ion-Exchange Loading Promoted Stability of Platinum Catalysts Supported on Layered Protonated Titanate-Derived Titania Nanoarrays

ACS Appl Mater Interfaces. 2019 Jun 19;11(24):21515-21525. doi: 10.1021/acsami.9b04378. Epub 2019 Jun 7.

Authors

Xingxu Lu, Wenxiang Tang, Shoucheng Du, Liaoyong Wen, Junfei Weng, Yong Ding¹, William S Willis², Steven L Suib², Pu-Xian Gao

Affiliations

¹ School of Materials Science and Engineering , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States.
² Department of Chemistry , University of Connecticut , Storrs , Connecticut 06269-3060 , United States.

PMID: 31132239
DOI: 10.1021/acsami.9b04378

Abstract

Supported metal catalysts are one of the major classes of heterogeneous catalysts, which demand good stability in both the supports and catalysts. Herein, layered protonated titanate-derived TiO₂ (LPT-TiO₂) nanowire arrays were synthesized to support platinum catalysts using different loading processes. The Pt ion-exchange loading on pristine LPTs followed by thermal annealing resulted in superior Pt catalysts supported on the LPT-TiO₂ nanoarrays with excellent hydrothermal stability and catalytic performance toward CO and NO oxidations as compared to the Pt catalysts through wet-impregnation on the anatase TiO₂ (ANT-TiO₂) nanoarrays resulted from thermal annealing of LPT nanoarrays. Both loading processes resulted in highly dispersed Pt nanoparticles (NPs) with average sizes smaller than 1 nm at their pristine states. However, after hydrothermal aging at 800 °C for 50 h, highly dispersed Pt NPs were only retained on the ion-exchanged LPT-TiO₂ nanoarrays with the support structure consisting of a mixture of 74% anatase and 26% rutile TiO₂. For the wet-impregnation loading directly on anatase TiO₂ nanoarrays derived from LPT, the Pt catalysts experienced severe agglomeration after hydrothermal aging, with the nanoarray supports consisting of 86% anatase and 14% rutile TiO₂. Spectroscopy analysis suggested that Pt²⁺ cations intercalated into the interlayers of the titanate frameworks through ion-exchange impregnation procedure, which altered the chemical and electronic structures of the catalysts, resulting in the shifts of the electronic binding energy, Raman bands, and optical energy bandgap. The ion-exchangeable nature of LPT nanoarrays clearly provides a structural modification in Pt-doped LPT that has resulted in a strong interaction between the Pt catalysts and LPT-TiO₂ nanoarray supports, leading to the enhanced hydrothermal stability of the catalysts. Considering the wide applications of the LPT and TiO₂ nanomaterials as supports for catalysts, this finding provides a new pathway to design highly stable supported metal catalysts for different reactions.

Keywords: hydrothermal aging; ion-exchange loading; layered protonated titanates; platinum catalysts; titania.